Actg2D245G Mutation Causes Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome by Impairing Smooth Muscle Contractility.

Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS; OMIM:619431) is a congenital disorder of the urinary and digestive systems that is caused by contractile dysfunction of smooth muscles. Recent studies have shown that ACTG2(HGNC:145) is the main gene involved in the pathogenesis of this disease. Herein, we aimed to investigate the correlation between the Actg2D245G mutation and disease phenotypes. We established an Actg2D245G mutant mouse model using the CRISPR/Cas9 system and performed voluntary urination tests, gastrointestinal (GI) motility analysis, collagen gel contraction, G-actin/F-actin ratio analysis, and three-dimensional structural simulations. Actg2D245G mutant mice exhibited weaker intestinal motility. The collagen gel contraction experiment revealed diminished contractility of smooth muscle cells, and G-actin/F-actin ratio analysis indicated impaired actin polymerization. Three-dimensional structural simulations demonstrated disrupted hydrogen bonds within the D245G mutant protein. Furthermore, intestinal and bladder dysfunctions caused by the Actg2D245G mutation were milder than those caused by the Actg2R257C mutation in mice. The Actg2D245G mutation affects intestinal motility by impairing actin polymerization and reducing cell contraction. The Actg2D245G mutation leads to milder disease phenotypes than the Actg2R257C mutation.